1. Field of the Invention
The present invention relates to a robot control apparatus for monitoring a load on a robot, in which a load exerted on a driving mechanism of a robot is monitored and utilized for a life prediction and a preventive maintenance of the robot.
2. Description of the Related Art
A driving mechanism of a robot usually employs mechanical elements such as a bearing and a speed reducer. A load exerted on these mechanical elements in the driving mechanism of the robot fluctuates unlike that in a general power unit. Therefore, it is difficult to predict the life of, and the time for the maintenance or overhaul of these mechanical elements.
As a deterioration analysis through robot torque analysis, there is known a method in which the change in the torque of a driving motor is used to predict a trouble from a pattern of the torque change. However, in this method, the torque including accelerating torque of a part such as the rotor of a motor is used, for evaluating a predication and is not used to find a torque actually loaded on a driving system. In order to predict a degradation and life of mechanical elements of a driving system of a robot, it is necessary to find a torque actually exerted on mechanical elements of a driving system. Furthermore, in this method, a pattern of an output torque of a motor is drawn using a plotter or the like to evaluate the pattern, so that the state of the load cannot be measured in real time during robot operation.
Also known is a method of finding a load exerted on the motor by determining the driving torque of the motor and the square mean thereof. This method, however, is for finding the load on the motor itself and for making a judgment to prevent the overheating and other troubles of the motor by averaging the power of the motor using the square mean and by comparing the average value and the rated torque of the motor.
Also, there is a method of finding the disturbance torque exerted on the driving system and arms from the driving current of the motor, which is, however, intended to estimate a sudden disturbance, and not intended to find the load torque of the driving system.
As described above, methods of prior art are not intended to find a load exerted on each part of a driving system nor suited for obtaining the data for a preventive maintenance or overhaul of each part of the driving system and for judging the life thereof. These methods are not for detecting a torque exerted on the driving system, and therefore the load torque exerted on the driving system has been estimated by operators based on their experience.